Heretofore, as cement dispersants, for example, polymelamine sulfonates, lignin sulfonates, copolymers of an olefin and maleic acid, and polycarboxylic acid-base dispersants have been used. However, due to various problems such as poor working efficiency at large building construction sites at which concrete mixer cars are forced to wait for a long period of time, lower profitability of suppliers of ready-mixed concrete since supply areas have to be decreased due to an inferior slump retention property, and in relation thereto, quality degradation which occurs when the time required for transportation of ready-mixed concrete is increased, improvement in slump retention has been always and enthusiastically required. Although polycarboxylic acid-base dispersants have a good slump retention property as compared that of previous generation cement dispersants, in the present circumstances in which the polycarboxylic acid-base dispersants have steadily and progressively spread in the related business fields, a slump retention property which is much superior to that of the current available dispersant has been strongly desired. In order to respond to this requirement, development of controlled-release polymers has been implemented for realizing a polymer which exhibits a slump retention property with time elapsed. Techniques relating to controlled-release cement dispersants have been disclosed. Patent Document 1 discloses palletized dispersants. Patent Documents 2 and 3 disclose a hydrolysable crosslink copolymer which makes use of an alkali condition in a cement dispersant liquid. Patent Document 4 discloses a time-release cement admixture containing poly(succinic imide). However, as for the techniques described above, improvement has been further desired in terms of product performance and effectiveness.
In addition, Patent Documents 5 and 6 disclose a copolymer containing a methacrylic acid ester and an acrylic acid ester. However, according to the documents mentioned above, the controlled-release performance using an alkali condition in a cement dispersant liquid has not been invented.
In addition, Patent Documents 7 and 8 disclose a carboxylic acid-base dispersant for high-strength concrete as a copolymer compound containing a polyamide polyamine or an alkylene oxide adduct thereof.                Patent Document 1: JP-A 54-139929        Patent Document 2: JP-A 03-075252        Patent Document 3: JP-A 06-157100        Patent Document 4: JP-A 08-169741        Patent Document 5: JP-A 9-40446        Patent Document 6: Japanese Patent No. 3029827        Patent Document 7: Japanese Patent No. 3235002        Patent Document 8: Japanese Patent No. 3336456        